del Potro backhand with a handful of inside out crosscourt forehands as well as crosscourt backhands.
Leading 1-0 breakpoint in set one, Isner struck a crosscourt forehand volley winner to break serve and go ahead 2-0.
Down 1-2 gamepoint in set two, Isner struck a 117 miles per hour down the line forehand winner; a forehand stroke faster than many serves, to hold serve and reach two games all.
Then serving down 4-5 with the crowd singing and chanting loudly in support of del Potro, the American struck serves at speeds of 133, 139 and 127 miles per hour to hold serve and reach five games all.
The set remained on serve to reach a decisive tiebreaker which saw Isner power towards an early 3-0 lead.
Serving ahead 3-2, Isner struck a 137 miles per hour serve out wide which forced a netted crosscourt backhand return from del Potro.
On the following point, Isner hit his 13th ace of the day down the tee at 139 miles per hour to lead 5-2 in the tiebreaker.
An Isner backhand down the line passing shot winner set up match point at 6-2.
Then after one hour and twenty-three minutes of play, Isner struck a crosscourt backhand volley winner to end the match.